Expiratory limit for a breathing circuit

ABSTRACT

A breathing circuit component includes an inlet, an outlet and an enclosing wall. The enclosing wall defines a gases passageway between the inlet and the outlet. At least a region of the enclosing wall is formed from a breathable material that allows the passage of water vapor without allowing the passage of liquid water or respiratory gases. The breathing circuit component may be the expiratory limb of a breathing circuit.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to components for breathing circuits andin particular to components for use in the expiratory arm of a breathingcircuit.

2. Summary of the Prior Art

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough conduits of a relatively restricted size. Buildup ofcondensation on the inside wall of the conduit is a frequent result ofthis high humidity. In the prior art, attempts have been made to reducethe adverse effect of this condensation by either reducing the level ofcondensation or providing collection points in the conduit for drainingcondensed liquid from the conduit. Reducing the condensation hasgenerally been by maintaining or elevating the temperature of the gasesflow and/or of the conduit wall to reduce the formation of condensation

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a component, withparticular application to the expiratory limb of a breathing circuit,which will at least go some way towards improving on the above or whichwill at least provide the public and the medical profession with auseful choice.

In a first aspect the invention consists in a breathing circuitcomponent including an inlet, an outlet and an enclosing wall defining agases passageway between said inlet and said outlet, at least a regionof said wall being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases.

In a further aspect the invention consists in a breathing circuit limbhaving both inspiratory and expiratory gases passageways, each having arespective inlet and outlet and a wall defining a gases passagewayextending from said inlet to said outlet, at least a region of the wallof the expiratory conduit being of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases.

In a still further aspect the invention consists in a catheter mountincluding:

a short length of breathing conduit for connecting at one end to apatient interface component and at the other end to, directly orindirectly, the dual arms of a breathing circuit,

a dividing partition extending for at least a substantial part of thelength of said breathing conduit and dividing, in cross section, saidconduit into a plurality of gases passageways each having a definingpassageway wall,

at least one of

an inspiratory flow director for directing at least the bulk of aninspiratory air flow to a first selection of said passageways, and

an expiratory flow director for directing at least the bulk of anexpiratory flow to a second selection of said passageways, said secondselection being exclusive of said first selection,

and at least a region of the walls of said second selection ofpassageways being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases.

In a still further aspect the invention consists in a dedicated watervapour exchanger including an inspiratory gases pathway and anexpiratory gases pathway having a common wall therebetween, said commonwall including one or more regions of a material that allows the passageof water vapour without allowing the passage of liquid water orrespiratory gases.

In a still further aspect the invention consists in apparatus forforming a breathing circuit conduit comprising:

a former, onto which a tube wall can be deposited and which advancessaid deposited tube wall in an advance axis and rotates said depositedtube wall about said advance direction, the speed of said advance andthe speed of said rotation together defining a pitch,

at least one film laying head which deposits a film on said former, thecombined width of said film deposited by said film laying heads beingwider than said pitch such that adjacent turns of laid film overlap toform an overlap seam,

a bead laying head for each said film laying head, each said bead layinghead laying a reinforcing bead on an overlap seam,

an axial thread laying head, said thread laying head fitted over andaround said former and carrying a plurality of thread feeds, each threadfeed allowing the drawing of a thread from a reserve, and

a rotator to rotate said axial thread laying head at substantially thesame speed as the expected rotation speed of said tube.

Hereinafter, throughout the description, a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases is described as a “breathable” material. Materials maybe breathable due to their composition, physical structure a combinationthereof.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional elevation of a conduit for the expiratorylimb of a breathing circuit according to one embodiment of the presentinvention,

FIG. 2 is a cross sectional view of a section of conduit wall accordingto one possible construction,

FIG. 3 is a cross sectional view of a co extrusion die head forextruding a conduit including two longitudinal strips of permeablematerial, similar to the conduit of FIG. 1,

FIG. 4 is a cross sectional elevation of a coaxial breathing circuitaccording to a further embodiment of the present invention andincorporating a conduit in accordance with the present invention,

FIG. 5 is a side elevation in partial cross section of the coaxialbreathing circuit of FIG. 4,

FIG. 6 is a side elevation partially in cross section of an expiratorylimb conduit according to a further embodiment of the present invention,

FIG. 7 is a cross sectional side elevation of an expiratory limb for abreathing circuit according to a further embodiment of the presentinvention,

FIG. 8 is a cross sectional side elevation of an expiratory limb for abreathing circuit according to a still further variant,

FIGS. 9a-9 i demonstrate a range of conduit constructions includinglongitudinal reinforcement of varying types,

FIG. 10 is plain view of a conduit forming device for forming areinforced twin walled conduit according to the present invention, suchas the conduit depicted in FIG. 9h or 9 i,

FIG. 11 is a plain view of a conduit forming device for forming areinforced conduit according to FIG. 7,

FIG. 12 is a plain view of a similar conduit forming device for forminga reinforced conduit according to FIG. 8, and

FIG. 13 is a cross sectional side elevation of a catheter mountincorporating the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1 in one embodiment of the invention the conduit 4 ofthe expiratory limb of a breathing circuit is formed having one or morelongitudinal strips 2, 3 of breathable membrane as part of the wall 1thereof.

One possible material for the breathable regions is an activatedperfluorinated polymer material having extreme hydrophilic properties.An example of this polymer material is marketed under the trade nameNAFION® by DuPont Fluoro products of Fayetteville USA. This material isuseful due to its extreme hydrophilic properties and due to its abilityto be extruded, particularly to be co-extruded in combination with otherplastic materials.

Alternative materials are also envisaged including:

(a) Hydrophilic thermoplastics,

(b) woven treated fabric products exhibiting breathable characteristics

The preferred material is a hydrophilic polyester block copolymer formedinto a homogeneous flat film. An example of such a film is sold underthe brand SYMPATEX®. This material is particularly suited to thin filmproductions.

Referring to FIG. 6 an alternative embodiment of the expiratory limb isshown in which the entire flexible wall membrane of the conduit isformed from a breathable plastic membrane, extruded and wound helicallywith edges of adjacent turns sealed to one another.

Further variations on the embodiment of FIG. 6 are depictured in FIGS.9a to 9 i, 7 and 8. In these figures the flexible wall membrane of theconduit is supplemented by reinforcing to provide resistance to lateralcrushing and to longitudinal stretching of the conduit. Furthervariations are shown including variants having multiple breathableplastic membranes. Apparatus for forming such conduits is described withreference to FIGS. 10, 11 and 12.

Referring to FIGS. 4 and 5 a further aspect of the present invention isshown in which an expiratory limb conduit according to the presentinvention is provided as the inner conduit of a coaxial conduitconfiguration, such that expiratory gases and inspiratory gases eachflow in one of the inner conduit or the space between the inner conduitand the outer conduit and in use water vapour but not liquid water istransmitted from the expiratory gases passageway to the inspiratorygases passageway.

A further component that may usefully include the present invention is acatheter mount. The application of the invention to a catheter mount isdescribed with reference to FIG. 13.

It would be possible alternatively, to have one or more longitudinalsections (lengths) of the conduit being formed of the breathablematerial or isolated regions of the conduit wall being formed from thematerial. However the embodiments described herein are preferred due totheir apparent simplicity of manufacture, being capable of linearmanufacture, either by continuous stitching, gluing or welding, by coextrusion or by winding onto a former.

As a corollary of material cost it is preferred that the conduit wall bemanufactured to have a relatively low wall thickness, so much so thatthe conduit wall membrane may be insufficiently sturdy to be selfsupporting.

Referring to FIGS. 2, 6, 9 a to 9 i, 7 and 8, a spiral or helicalinternal (or external) reinforcing members, or a series of annular hoopreinforcing members, may be provided outside (or inside) the tubularmembrane to provide support. The helical, spiral or hoop supportingmembers may for example be formed from polymer plastic materials, suchas the material used in the wall of the conduit (not being thebreathable regions), or alternatively may for example be a metal wiresupport, such as drawn steel wire.

The conduit shown in FIG. 2 may be formed in any one of a number ofmethods. For example the tubular membrane may be supplied in acontinuous tube. Alternatively it might be supplied in tape form, whichmay result in the conduit of FIG. 6. Supplied as extruded tape, themembrane may be wound helically onto a former. The helical supportingrib, provided in a semi molten state is then laid on the overlap betweenadjacent turns. The heat from the helical supporting rib bonds the twoadjacent strips with the rib forming a flexible resilient conduit oncecooled.

Referring to FIG. 6 an additional sheathing layer 83 may be providedover the outside of the conduit. The sheathing layer 83 is supported onthe apexes of the ribs 30. The sheathing layer 83 may be a further stripor tape of extruded plastic film wound helically onto the conduit formedon the former. This additional sheath may have a number of purposes andbenefits. The sheathing layer 83 may be formed to provide additionalstrength, reinforcement and protection, for example by selecting anappropriate material or by selecting an appropriate material thickness.The material may be a breathable material, such as that which may be thebasis of the inner conduit wall or may be formed from a less expensivenon-permeable material. In that case a series of holes or perforations85 are preferably provided along the strip or tape 84 to provide egressof water vapour or collected condensed water. The holes or perforations85 may advantageously be formed by pricking holes in the tape 84 using aheated lance during the forming process. Shrinking of the plastic filmaway from the heated lance has been found to produce consistent andsuitably sized holes with an annulus of built up material providingreinforcing at the lip of the hole. The sheath 83, in addition toproviding reinforcement and protection for the inner conduit, alsoprovides a barrier to air flow over the inner conduit thereby providingan insulating effect. The insulating effect is greater where there areno perforations 85 through the sheath 83.

Referring to FIGS. 9a-9 i it has been found that one of the difficultieswith using a breathable membrane such as a SYMPATEX®membrane is its lowelastic yield strength. Accordingly under longitudinal force theSYMPATEX® membrane may be easily stretched non-elastically leading toloss of aesthetic appearance and a constriction in the tube diameter.The multiple walled embodiment described with reference to FIG. 6 goessome way toward overcoming this difficulty, providing as it does asecond layer of breathable material. Furthermore in the perforated formthe outer plastic membrane may be formed from a plastic material havinga greater elastic yield strength than the preferred SYMPATEX®membrane.

An alternative structure may be used as a longitudinal reinforcement forthe tube. This reinforcement is preferably provided in a form of anadditional sheath having an open or mesh structure. For example thesheath may be provided by a plurality of parallel extruded polymerthreads running parallel to the axis of the conduit, a plurality ofextruded polymer threads braided or similarly arranged about the conduitand having a substantial axial component in their direction, or by apreformed or continuously formed mesh, formed to make a sheath in asimilar fashion to the method used for forming the breathable wall. Sucha mesh material may be produced by forming a non-woven or woven mesh ofindividual polymer threads or by stretching a micro perforated sheet tomake an expanded mesh, or by other suitable processes. Part or each ofthese processes may be conducted at the time of, or immediatelypreceding, using the mesh in forming the reinforcing sheath.

A variety of alternative conduit embodiments incorporating a reinforcingsheath, such as introduced above, are depicted in FIGS. 9a to 9 i. Twoother preferred forms are depicted in FIGS. 7 and 8. These embodimentshave various advantages and/or disadvantages.

Referring to FIG. 9a a conduit is formed from an extruded tape 200helically wound on a former to form the breathable wall. A mesh sheath202 is formed from a mesh tape helically wound onto the outside of thebreathable membrane 200. The overlapping edges of the mesh tape and thebreathable membrane tape coincide and a molten plastic bead 201 is laidalong these edges. The molten bead preferably provokes thermal bondingof all four coinciding layers, two of breathable membrane and two ofpolymer mesh. It will be appreciated that the polymer mesh may be on theinside or outside of the breathable membrane. However it is preferredthat the internal surface of the conduit wall be smooth and hence it ispreferred that the mesh tape be applied to the outside of the breathablemembrane. It will be appreciated that each turn of mesh tape may beapplied directly over each turn of breathable membrane contemporaneouslyso that the edges of adjacent turns overlap an edge of mesh tape comesbetween the edges of adjacent turns of breathable membrane tape, whichis alternative to how it is depicted in FIG. 9a. It will also beappreciated that either or both of the breathable membrane tape and themesh tape may be formed contemporaneously with forming the conduittherefrom and the mesh and membrane may accordingly bond over some orall of their contacting surfaces in addition to bonding achieved by heatfrom the bead 201.

Referring to FIG. 9b a conduit is formed having the same construction ofbreathable membrane 200, mesh 202 and bead 201. In addition a furthersheath of breathable membrane 203 may be applied to the outside of theconduit, with the edges of adjacent urns 203 pressed onto and bonded tothe outside of bead 201. This provides additional thermal insulationwhile allowing for dehumidification of the space between the inner andouter walls.

Referring to FIG. 9c the conduit of 9 a is shown having breathablemembrane wall 200, mesh sheath 202 and bead 201. In the embodiment ofFIG. 9c a further breathable membrane sheath 204 is provided on theoutside of the mesh sheath 202. The effect of this is to encapsulate themesh 202 providing an improved aesthetic appearance and more acceptableexternal surface. A disadvantage of his constriction is the multitude oflayers which the heat from bead 201 is required to thermally bond.Accordingly a construction of this type may require additional localisedheating to thermally weld the overlapping edges of adjacent turns ofmembranes 200, 202, and 204.

Referring to FIG. 9d a variation on the embodiment shown in FIG. 9c isdepicted. In this embodiment the outer breathable membrane 205 isinflated away from the mesh membrane 202 where in FIG. 9c the outerbreathable membrane 204 lay against or bonded with the mesh membrane202. In FIG. 9d the breathable 205 is supported away from the underlyingmembranes 200, 202 by an inflated pocket 211. This may be considered avariant of FIG. 9b wherein the bead 201 is provided entirely on theoutside of the conduit. The multitude of layers at adjoining edges posesthe same forming difficulties as the embodiment of FIG. 9c.

Referring to FIG. 9e a section of the conduit in which the mesh sheathis provided spaced from the breathable membrane conduit wall 200. Themesh sheath 206 is provided over the bead 201 at least in the vicinityof the joining of adjacent turns of the breathable membrane 200. Wherethe mesh sheath is formed from a wound tape then adjacent turns 206 ofthe wound tape bond over the bead 201 upon action of the heat residingin the bead 201. This embodiment reduces the number of adjacent layersrequired to be bonded by the bead 201 and allows the layers ofbreathable membrane and mesh respectively to operate independentlymaking this tube more supple than for example for tube in FIG. 9a.

FIG. 9f is a variation of the embodiment of FIG. 9e. While an air spacewas provided between the mesh layer 206 and the breathable membranelayer 200 in FIG. 9e, in FIG. 9f the mesh layer 207 is shrunk, vacuumedor collapsed to lie adjacent the breathable membrane layer 200. Whereone or more of the breathable membrane and mesh are formedcontemporaneous with forming of the conduit then where these layers 207and 200 meet they may bond across some or all of their contacting area.This embodiment provides the formative advantages of FIG. 9e and aconstruction having similar qualities to that of FIG. 9a.

Referring to FIG. 9g, in a further embodiment, an additional breathablemembrane is provided to the embodiment of FIG. 9f, spanning between tunsof bead 201 and the outside of the mesh 207. To assist with bonding andfor further reinforcement purposes a further bead 209 may be provided onthe outside of the second breathable layer 208.

Referring to FIG. 9h a still further embodiment is shown which is avariation of the embodiment shown in FIG. 9g. In the embodiment of FIG.9h a second layer of breathable membrane 210 is provided on the outsideof second bead 209. This is instead of being between the second bead 209and the mesh layer 207 as the second breathable layer 208 was in theembodiment FIG. 9g. This provides a larger included air space betweenbreathable layers 202 and 210 and at any time only a double thickness ofpolymer, film or mesh is required to be bonded by the beads 201 or 209.

Referring to FIG. 9i a still further embodiment is shown, being avariation of the embodiment shown in 9 h. In the embodiment of 9 i themesh layer 206 rather than being the deflated, collapsed or vacuumedform as in FIGS. 9f-9 h, it is taut between turns of bead 201, in thefashion of 9 e. This provides a pair of air spaces between thebreathable layers 200 and 210, with the mesh layer 206 partiallyinhibiting the free air flow between the layers. However, thisconstruction has the disadvantage that the freely suspended mesh 206 mayencourage rain out in the space enclosed between the breathablemembranes 200 and 210, thereby retaining liquid water within the helicalwall cavity.

All of the above described configurations are considered to provideadditional longitudinal reinforcement, with each having advantages anddisadvantages, some of which have been specified. In forming theseconstructions bonding is required between some or all of the variouslayers, for example between the breathable membrane and one or otherbead, the bead and the mesh, the mesh and breathable membrane.Accordingly, it is preferred that appropriately compatible materials areused for each element of the construction. For example while a moltenpolyester bead may mechanically bond adequately with nylon orpolypropylene mesh a brittleness my develop and/or this impeded thesimultaneous bonding of the bead with an adjacent layer of polyesterbased breathable membrane, for example in the embodiment of FIG. 9a.Consequently it is preferred that all three elements have the same basepolymer, and for example, for a SYMPATEX® membrane which is polyesterbased product, a polyester bead and a mesh are preferred.

Further variations on the above embodiments may include replacement ofthe outer breathable layer in FIGS. 9b,c,d,g,h and i with a perforatednon permeable layer, as desired. However, such variation does notprovide the full insulative effect while retaining liquid vapourtransmission from the insulating space to allow for further transmissionthrough the conduit wall.

An example of forming apparatus suitable for manufacturing the productthe breathing tube according to the embodiments described in FIGS. 9a-9i is shown in FIG. 10. In particular the apparatus is shown forming aconduit according to FIG. 9h or 9 i. The apparatus includes a former 300preferably of a known type including a plurality of rotating rodsarranged around a central support rod. The rods extend from and arerotated by a gearbox within a machine stock 301. At least in the tubeforming region the rotating rods follow a helical path. The pitch angleof the rods relative to the support rod controls the pitch angle of thetube being formed. An example of such a machine is a spiral pipelinemandrel available from OLMAS SRL of Italy. Tube being formed on theformer is rotated and advanced in the direction of arrow 303 by themovement of the rotating rods. The advance speed of the former isselected relative to the rotational speed so that the pitch of thehelical laying of the strip or tape on to the former 300 is a littleless than the width of the strip so that adjacent turns narrowlyoverlap. A first extruder 304 extrudes a tape 314 of breathable polymermaterials. The tape 314 deposits on the former 300 in a helical fashionby action of the former. The pitch of the helical disposition of tape314 is slightly less than the width of tape 314. The helical depositionof tape 314 forms the inner breathable wall 200 of the conduit. A secondextruder 305 extrudes a bead 315 of polymer material. The bead 315deposits on the former over the joint or overlap between adjacent turnsof tape 314 forming a raised bead 201 along this join. A tape 316 ofreinforcing membrane is unrolled from a reel 306 to have edgesdepositing on adjacent tuns of bead 201. The helically depositedreinforcing tape 316 forms reinforcing layer 206. A third extruder 307extrudes a second molten polymer bead 317. The bead 317 is helicallydeposited along the overlap between adjacent turns of reinforcing tape316. A fourth extruder 308 extrudes a second tape 318 of breathablepolymer. The second tape 318 of breathable polymer is deposited on theformer 300 to span between adjacent turns of second bead 317. Adjacentus of tape 318 overlap while sufficiently molten to fuse above thesecond bead 209, forming outer breathable sheath 210.

In addition to the bonding of the film overlap by application of themolten bead other active fusing techniques may be applied. This may beparticularly useful where a layer of longitudinal reinforcement or scrimis provided immediately adjacent the breathable film layer. Activemethods may include hot air welding, hot rollers or radio frequencywelding. In hot air welding a stream of hot air is blown on to theoverlap of adjacent turns of breathable film, melting or fusing theadjacent edges together. This method has been found reasonablysuccessful.

For hot roller welding a heated roller or rollers run in contact withthe overlap and melt the film together. Like hot air welding hot rollerwelding relies on the application of a localised direct heating to thefilm overlap.

For radio frequency welding the film acts as an insulation layer betweena pair of plates. A charge is passed between the plates melting andfusing the plastic film overlap together. The plates may take the formof a pair of rollers, one inside and one outside the tube, or a rollerand one of the rotating rods of the former. Providing the plates asrollers (or as roller and forming mandrel) may render the radiofrequency welding a continuous process with similar advantages to hotair welding and hot roller welding.

In a further variation on the manufacturing process the breathable filmtube may be manufactured having a longitudinal seam rather than beingformed as a continuous helical strip. In such an embodiment a wider webof film would be wrapped around a mandrel as it is extruded or unrolledfrom a reel. Longitudinal edges would overlap and be seam welded by anyof the above mentioned methods. A rotary extruder may then extrude areinforcing bead or beads on to the plastic film. Further reinforcing orfilm layers and helical beads may be applied by additional wrappingstations or rotating extruders as required.

Still further embodiments of a expiratory breathing conduit includinglongitudinal reinforcement are depicted in FIGS. 7 and 8. Theseembodiments utilise longitudinal reinforcing threads running parallel tothe axis of the conduit.

In the embodiment of FIG. 7 the conduit includes an inner breathablepolymer wall 250 with a plurality of axially extending reinforcing reads251 running the length of said wall and spaced around the perimeter ofthe tube. The threads 251 are aligned parallel to one another and to themajor axis of the conduit. A layer of additional longitudinalreinforcement 252, such as described earlier, and which may be a wovenor non woven mesh, aligned in any suitable orientation (althoughpreferably aligned with the principal threads running at an angle to themajor axis of said conduit) encloses the breathable permeable wall andreinforcing threads. A helical bead 253 is fused or adhered to theoutside of the mesh 252.

A preferred method of forming the tube according to the embodiment ofFIG. 7 is described with reference to the apparatus shown in FIG. 11. Inparticular in the apparatus of FIG. 11 both the inner, breathable, tube250 and longitudinal reinforcement layer 252 are formed by helicallywrapping a preformed tape or strip of the base material (breathablepolymer strip 260 or mesh strip 262 respectively) on to a rotatingformer 270 (such as described earlier with reference to FIG. 10). Thestrip 260 or 262 unrolls from reels 273 and 274 respectively. Adjacentturns of breathable polymer 260 overlap at their edges. Theseoverlapping edges are fused by thermal welding. Thermal welding isconducted as a continuous process by a hot air welding head 275.Rotation and advancement of the former 270 by the rotation head 271continually passes the seam between adjacent edges of tape 260 past thehead 275. A freely rotatable thread laying head 276 is located over theformer 270 at a position between the hot air welding head 275 and themesh spool 274. The rotating head 276 carries a plurality of spools 279holding the reinforcing threads 251. The head 276 is rotatable by anelectric motor and drive belt 277 and 278 respectively. The head 276 ispreferably rotated at a speed synchronized with the speed of rotation ofthe former 270. Advancement of the former 270 draws thread 280 from thespools 279 to be laid as parallel threads 251 on the outside of thebreathable membrane 250. The tape 262 of longitudinal reinforcement issubsequently applied over the threads 251 as a helical arrangement withedges of adjacent turns overlapping to form a continuous sheath. A bead263 is extruded by an extruder 281 on to the overlap between adjacentturns of the mesh tape 262 to thereby form the helical reinforcing bead253.

This embodiment of the invention provides a breathable exhalation limbreinforced against crushing by the helical bead and against longitudinalextension by the axial threads 251. The mesh sheath 252 protects theaxial threads from snagging or pulling.

In the embodiment of FIG. 8 the conduit includes an inner breathablepolymer wall 350. A helical bead 353 is fused or adhered to the innerbreathable wall 350. A plurality of reinforcing threads 251 running thelength of the wall and spaced around the perimeter of the tube arealigned parallel to one another and to the major axis of the conduit.The threads 351 are supported on the helical bead 353, with the threadsspanning the spaces between turns of the helical bead. In thisembodiment it is important to choose the reinforcing threads (material,gauge and number) such that the threads are sufficiently stiff to resistbuckling under the transiently reduced internal pressures that could beexpected during patient breathing. Unrestrained or excessive buckling ofthe threads could lead to unacceptable levels of conduit axialcontraction. The axial threads 351 may be a spun or braided fibres,drawn or extruded mono filaments or other equivalent forms.

A preferred method of forming the tube according to the embodiment ofFIG. 8 is described with reference to the apparatus shown in FIG. 12. Inparticular in the machine of FIG. 12 the breathable tube 350 is formedby helically wrapping a preformed tape or strip of breathable polymerstrip 360 on to a rotating former 370. The strip 360 unrolls from reels373. Adjacent turns of breathable polymer 360 overlap at their edges.These overlapping edges are fused by thermal welding. Thermal welding isconducted as a continuous process by a hot air welding head 375.Rotation and advancement of the former 370 continually passes the seambetween adjacent turns of tape 360 past the head 375. A bead 363 isextruded by an extruder 81 on to the overlap between adjacent turns ofthe breathable tape 362 to thereby form the helical reinforcing bead353. A freely rotatable threadlaying head 376 is located over the formerafter the bead extruder 381. The rotating head 376 carries a pluralityof spools 379 holding the reinforcing threads 351. The head 376 isrotatable by an electric motor and drive belt 377 and 378 respectively.The head 376 is preferably rotated at a speed synchronized with thespeed of rotation of the former 370. Advancement of tube along theformer 370 draws thread 380 from the spools 379 to be laid as parallelthreads 351 on the outside of the reinforcing bead.

This embodiment of the invention provides a breathable exhalation limbreinforced against crushing by the helical bead and against longitudinalextension by the axial threads 351. The spanning threads prevent directcontact between a user and the surface of the breathable tube, reducingthe risk of punctures and the like.

It should be appreciated that with all of the forming methods involvingwinding of a narrow tape or strip to create a tube, it would be possibleto wind two or more tapes or strips simultaneously onto the former sothat the turns created by each tape are interposed by turns of othertapes, edges overlapping and being bonded together. For example a pairof tapes may be laid as a double helix. This would require amultiplication in the number of forming stations associated with thewound on components of the tube or conduit.

Referring to FIG. 3 other forms of the conduit, such as that shown inFIG. 1, may be formed by co extrusion of the breathable material (wherethe material is a suitable extrudable material) with a plastic materialforming the remainder of the conduit wall. A suitable co extrusion die 9is depicted in FIG. 3 in which a pair of circumferential sections 7 ofthe die opening have the breathable plastic material extrudedtherethrough, and the remainder sections 8 of the annular extrusionopening have the non permeable plastic wall material extrudedtherethrough.

The purpose of the breathable region or regions of the conduit wall isto allow diffusion of water vapour from the expiratory limb of thebreathing circuit along the path thereof independent of specific drainlocations. This eliminates the build up of condensation within theexpiratory limb by drying the humidified gases during their flow throughthe expiratory limb. This furthermore reduces the humidity of the gasesarriving at ancillary equipment, such as filters, ventilators and thelike reducing the risk of condensation accumulation, thereby improvingtheir operation.

In accordance with a further aspect of the invention, and as exemplifiedin FIGS. 4 and 5 the conduit incorporating one or more longitudinalstrips of breathable membrane may further be incorporated in a coaxialbreathing circuit as a passive humidification device. In particularreferring to the cross section in FIG. 4 the coaxial breathing circuitmay include an outer conduit 11 and an inner conduit 10. Preferably, forheat transfer reasons, the inner conduit 10 carries the inspiratory flowin the space 12 there within. The expiratory flow is preferably carriedin the space 13 between the inner conduit 10 and the outer conduit 11.This airflow configuration is indicated by arrows 20, 19 respectively inFIG. 5.

The inner conduit 10 is formed having one or more longitudinal strips 2,3 of breathable membrane in the wall 1 thereof, as has previously beendescribed with reference to FIGS. 1, 2 and 3. Thus humidity in theexpiratory flow space 13 may pass through the sections 2, 3 ofbreathable membrane to humidify the inspiratory flow in inspiratory flowspace 12.

The breathable membrane works on relative partial pressures of watervapour so, with the flows in a counter flow arrangement substantialpassive humidification of the inspiratory flow can be achieved.

Referring to FIG. 5 a circuit configured including the coaxial conduitdepicted in FIG. 4 is represented. In this circuit the conduit has apatient end connector 15 and a ventilator end connector 16 havinginspiratory port 17 and an expiratory port 18. The inspiratory 20 andexpiratory 19 counter flows are indicated.

With the coaxial conduit the ventilator may not become aware of the leakin the interior conduit. Such a leak may short circuit the patientmeaning that the patient will not be supplied with sufficient oxygen.Such a short circuit may be detected by placement of a sensor at thepatient end. Preferably this sensor may be located in the patient endconnector 15. A short circuit closer to the ventilator will lead tocontinued patient rebreathing of the air volume close to the patient.This will lead to a rise in the concentration of carbon dioxide in theconduit close to the patient which can be detected directly by a CO²sensor. Such a sensor may comprise any one of a number of such sensorsas is currently commercially available. Alternatively this re breathingmay be detected by monitoring the temperature of the gases at thepatient end connector 15, wherein a rise in temperature above apredetermined level indicates that rebreathing is occurring.

In addition to the above to reduce or eliminate the formation ofcondensation within either the inner or outer conduit, 10 or 11respectively, and to maintain a substantially uniform temperature in thegases flow through the conduit, a heater means, such as a resistanceheater wire, may be provided within either the inner or outer conduit,disposed within the gases spaces 12 or 13 or within the conduit wallsthemselves. In one possibility the heater wire may also serve as areinforcing support (helical wire 25 in FIG. 4) within the inner conduit10 or in the outside conduit as with coaxial conduit.

A further breathing circuit component to which the present invention canbe applied is catheter mounts. A catheter mount connects between apatient interfacing component such as a mouth piece, nasal mask orendotracheal tube and the dual limbs of a breathing circuit. Connectionwith the dual limbs of the breathing circuit is generally via a wyeconnector. In the patient inhalation and exhalation cycle the dual limbsof the breathing circuit each have a distinct role, one as inhalationconduit and one as exhalation conduit. The catheter mount serves a dualrole, transporting both inhaled and exhaled gases. Accordingly, thecatheter mount can have significant disadvantages.

A volume of exhaled air remains in the catheter mount between exhalationand inhalation. Accordingly some air is re-breathed by the patient.While not unacceptable, rebreathing is not generally desirable and wheresignificant rebreathing is likely, a boost in oxygen supply levels maybe required.

Gases inhaled by a patient are, in a well managed ventilation system,delivered in a condition having humidity near a saturation level and atclose to body temperature, usually at a temperature between 33° C. and37° C. This temperature may be maintained by a heater in the inhalationconduit right up to the point where the gases enter the catheter mount.Gases exhaled by a patient are returned fully saturated and aresubjected to further cooling as they flow through the catheter mount.Accordingly, although little condensation forms on the interior wallsduring patient inhalation, significant condensation levels may formduring patient exhalation. The condensation, or rain out, occurringinside the catheter mount is particularly deleterious due to itsproximity to the patient. Mobile condensate breathed or inhaled by apatient may lead to coughing fits or other discomfort.

A catheter mount incorporating the present invention is depicted in FIG.13. The catheter mount incorporates the wye connector at the ventilatorend. An internal conduit 455 extends coaxially with the outer conduit456. The internal conduit 455 is supported at its patient end on ainternal conduit connector 457 which is turn is supported via supportstruts 458 from patient end connector 459. The inner conduit 455 issupported at its other end on an inner conduit connector 460 which formspart of the ventilator end connector 461.

In the catheter mount of FIG. 13 the ventilator end inner conduitconnector 460 communicates with the inspiratory conduit connector 462.The outer conduit 456 has at least a part of its wall being made from abreathable material. Preferably the outer conduit 456 is formed entirelyfrom breathable material, and may also include lateral reinforcement (aspiral reinforcing bead 467) and longitudinal reinforcement (axiallyoriented threads 490) on the outside thereof. When constructed accordingto the manner earlier described with respect to FIGS. 12 and 8 thespiral bead 467 is laid on the overlap between consecutive turns of theextruded tape and assists fusion of the overlap and reinforcementagainst crushing.

Therefore in use the catheter mount according to FIG. 13 has aninspiratory flow entering the catheter mount as indicated by arrow 470.The inspiratory flow passes through the inner conduit to exit to thepatient through the patient end connector 459 as indicated by arrows471. Upon patient exhalation, whether assisted or otherwise, expiredgases pass through connector 459 and into the space surrounding theinner conduit 455 as indicated by arrows 472. These gases pass along theinside of the wall of outer conduit 456 as indicated by arrows 473 andout through the expiratory tube connector 463 of ventilation connector461 as indicated by arrow 474. In passing through the catheter mountwithin the space between the inner conduit 455 and the outer wall 456water vapour may pass through the water vapour permeable portions of theouter conduit 456. Preferably the entire of outer conduit 456, apartfrom any reinforcing rib, is breathable. In this way, although theexpired gases may experience some temperature drop as they pass throughthe catheter mount to the expiratory conduit connector 463, hand in handwith this temperature drop is a reduction in humidity by water vapourpassing through the breathable membrane of the outer conduit.Accordingly, relative saturation of the expiratory flow is reduced andrain out is reduced.

The catheter mount incorporating features according to the presentinvention includes explicit division of the inspiratory and expiratoryflows through the catheter mount—significantly reducing rebreathing.Rain out is also reduced by reducing the humidity of the expired gaseseven as the temperature of those gases reduces.

While some embodiments of the present invention have been described aspreferred and convey particular advantages over other embodiments manyother combinations may prove commercially useful.

What is claimed is:
 1. A breathing circuit component including an inlet,an outlet and an enclosing wall defining a gases passageway between saidinlet and said outlet, at least a region of said wall being of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases, and said gases passagewayis an expiratory conduit and said region or regions is or aredistributed over the length of said conduit, and said conduit includesat least one helically wound polymer tape or strip, part or all of saidstrip being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases,respective edges of adjacent turns of said strip being adjoining oroverlapping and bonded, and said conduit includes lateral reinforcementagainst crushing wherein said lateral reinforcement is a helical beaddisposed over said adjoining or overlapping edges between turns ofstrip, and said conduit includes longitudinal reinforcement againstlongitudinal stretching of said conduit.
 2. A breathing circuitcomponent as claimed in claim 1 wherein said longitudinal reinforcementincludes a plurality of longitudinally extending threads spaced aroundthe perimeter of the conduit wall, each said thread alignedsubstantially parallel with the overall axis of said tube and saidthreads are supported away from said conduit wall by said helical bead.3. A breathing circuit component as claimed in claim 2 wherein saidthread is bonded to said bead at crossings of said bead, and spans thegaps between adjacent turns of said bead.
 4. A breathing circuitcomponent as claimed in claim 2 wherein said longitudinal reinforcementincludes an outer sheath disposed about said conduit and supported onsaid bead.
 5. A breathing circuit component as claimed in claim 4wherein said outer sheath includes at least region which are of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases.
 6. A breathing circuitcomponent as claimed in claim 4 wherein said outer sheath has aplurality of holes or apertures therethrough.
 7. A breathing circuitcomponent as claimed in claim 1 wherein said longitudinal reinforcementincludes an outer sheath disposed about said conduit and bonded withsaid conduit wall.
 8. A breathing circuit component as claimed in claim7 wherein said outer sheath is bonded to said conduit wall by action ofa helical bead.
 9. A breathing circuit component as claimed in claim 8wherein said outer sheath includes a plurality of longitudinallyextending polymer threads, either parallel with the axis of said conduitor braided about said conduit.
 10. A breathing circuit component asclaimed in claim 1 wherein where said longitudinal reinforcement issupported on said bead from said first wall, a second bead is disposedover said first bead, and paid longitudinal reinforcement is heldbetween said first and second beads.
 11. A breathing circuit componentas claimed in claim 10 including a further said wall of a material thatallows the passage of water vapour without allowing the passage ofliquid water or respiratory gases disposed on the outer surface of saidsecond bead.
 12. A breathing circuit component as claimed in claim 10including a further said conduit wall of a materiel that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases adjacent said longitudinal reinforcement and betweensaid first and second beads.
 13. A breathing circuit limb having bothinspiratory and expiratory gages passageways, each having a respectiveinlet and outlet and a wall defining a gases passageway extending fromsaid inlet to said outlet, at least a region of the wall of theexpiratory conduit being of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, and wherein one said gases passageway is defined by an innerconduit, said inner conduit is disposed substantially coaxially withinan external surrounding conduit, and the other of said gases passagewaysis defined between the inner and outer conduits, and wherein saidconduit includes at least one helically wound polymer tape or strip,part or all of said strip being of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, respective edges of adjacent turns of said strip being adjoiningor overlapping and bonded, and said conduit includes lateralreinforcement against crushing and said lateral reinforcement is ahelical bead disposed over said adjoining or overlapping edges betweenturns of strip, and said conduit includes longitudinal reinforcementagainst longitudinal stretching of said conduit.
 14. A breathing circuitlimb as claimed in claim 13 wherein said longitudinal reinforcementincludes a plurality of longitudinally extending threads spaced aroundthe perimeter of the conduit wall, each said thread alignedsubstantially parallel with the overall axis of said tube and saidthreads are supported away from said conduit wall by said helical bead.15. A breathing circuit limb as claimed in claim 14 wherein said threadis bonded to said bead at crossings of said bead, and spans the gapsbetween adjacent turns of said bead.
 16. A breathing circuit limb asclaimed in claim 14 wherein said longitudinal reinforcement includes anouter sheath disposed about said conduit and supported on said bead. 17.A breathing circuit limb as claimed in claim 16 wherein said outersheath includes at least regions which are of a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases.
 18. A breathing circuit limb as claimed in claim 16wherein said outer sheath has a plurality of holes or aperturestherethrough.
 19. A breathing circuit limb as claimed in claim 13wherein said longitudinal reinforcement includes an outer sheathdisposed about said conduit and bonded with said conduit wall.
 20. Abreathing circuit limb as claimed in claim 19 wherein said outer sheathis bonded to said conduit wall by action of a helical bead.
 21. Abreathing circuit limb as claimed in claim 20 wherein said outer sheathincludes a plurality of longitudinally extending polymer threads, eitherparallel with the axis of said conduit or braided about said conduit.22. A breathing circuit limb as claimed in claim 13 wherein where saidlongitudinal reinforcement is supported on said bead from said firstwall, a second bead is disposed over said first bead, and saidlongitudinal reinforcement is held between said first and second beads.23. A breathing circuit component including an inlet, an outlet and anenclosing wall defining a gases passageway between said inlet and saidoutlet, at least a region of said wall being of a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases, and said gases passageway is an expiratory conduitand said region or regions is or are distributed over the length of saidconduit, and said conduit includes at least one helically wound polymertape or strip, part or all of said strip being of a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases, respective edges of adjacent turns of said stripbeing adjoining or overlapping and bonded, and said conduit includeslongitudinal reinforcement against longitudinal stretching of saidconduit.
 24. A breathing circuit component as claimed in claim 23wherein said longitudinal reinforcement includes a plurality oflongitudinally extending threads spaced around the perimeter of theconduit wall, each said thread aligned substantially parallel with theoverall axis of said tube.
 25. A breathing circuit component includingan inlet, an outlet and an enclosing wall defining a gases passagewaybetween said inlet and said outlet, at least a region of said hall beingof a material that allows the passage of water vapour without allowingthe passage of liquid water or respiratory gases, and wherein said gasespassageway is an expiratory conduit and said region or regions is or aredistributed over the length of said conduit, and wherein said conduitincluding said regions is extruded, and wherein said regions of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases are one or morelongitudinal strips running the complete length of said conduit, andsaid conduit includes lateral enforcement against crushing, and saidlateral reinforcement is helical bead or a series of annular ring beadsor ribs distributed over the length of said conduit, and said conduitincludes a further wall of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, and said further wall is spaced from said enclosing wall by atleast said helical bead.
 26. A breathing circuit limb having bothinspiratory and expiratory gases passageways, each having a respectiveinlet and outlet and a wall defining a gases passageway extending fromsaid inlet to said outlet, at least a region of the wall of theexpiratory conduit being of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, and wherein one said gases passageways is defined by an innerconduit, said inner conduit is disposed substantially coaxially withinan external surrounding conduit, and the other of said gases passagewaysis defined between the inner and outer conduits, and wherein saidconduit includes at least one helically wound polymer tape or strip,part or all of said strip being of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, respective edges of adjacent turns of said strip being adjoiningor overlapping and bonded, and said conduit includes longitudinalreinforcement against longitudinal stretching of said conduit.
 27. Abreathing circuit limb as claimed in claim 26 wherein said longitudinalreinforcement includes a plurality of longitudinally extending threadsspaced around the perimeter of the conduit wail, each said threadaligned substantially parallel with the overall axis of said tube.
 28. Abreathing circuit limb as claimed in claim 27 including a further saidwall of a material that allows the passage of water vapour withoutallowing the passage of liquid water or respiratory gases disclosed onthe outer surface of said second bead.
 29. A breathing circuit limb asclaimed in claim 27 including a further said conduit wall of a materialthat allows the passage of water vapour without allowing the passage ofliquid water or respiratory gases adjacent said longitudinalreinforcement and between said first and second beads.
 30. A breathingcircuit limb having both inspiratory and expiratory gases passageways,each having a respective inlet and outlet and a first wall defining agasses passageway extending from said inlet to said outlet, at least aregion of said first wall of the expiratory conduit being of a materialthat allows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, and wherein one said eases passagewayis defined by an inner conduit, said inner conduit is disposedsubstantially coaxially within an external surrounding conduit, and theother of said eases passageways is defined between the inner and outerconduits, and wherein said conduit including said regions is extruded,and wherein said regions of a material that allows the passage of watervapour without allowing the massage of liquid water or respiratory gasesare one or more longitudinal strips running the complete length of saidconduit, and said conduit includes lateral reinforcement againstcrushing, and wherein said lateral reinforcement is a helical bead or aseries of annular ring beads or ribs distributed over the length of saidconduit, and said conduit includes a further wall of a material thatallows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, and said further wall is spaced fromsaid first wall by at least said helical bead.
 31. A breathing circuitcomponent including an inlet, an outlet and an enclosing wall defining agases passageway between said inlet and said outlet, at least a regionof said wall being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases, andsaid gases passageway is an expiratory conduit and said region orregions is or are distributed over the length of said conduit, and saidconduit includes at least one longitudinal strip, part or all of saidstrip being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases, saidstrip or strips extending parallel to the axis of said conduit, edges ofsaid strip or strips adjoining or overlapping to form an enclosed tubeand bonded, and said conduit includes longitudinal reinforcement againstlongitudinal stretching of said conduit.
 32. A breathing circuitcomponent as claimed in claim 31 wherein said longitudinal reinforcementincludes a plurality of longitudinally extending threads spaced aroundthe perimeter of the conduit wall, each said thread alignedsubstantially parallel with the overall axis of said tube.
 33. Abreathing circuit component including an inlet, an outlet and anenclosing wall defining a gases passageway between said inlet and saidoutlet, at least a region of said wall being of a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases, and said gases passageway is an expiratory conduitand said region or regions is or are distributed over the length of saidconduit, and said conduit is a blown film tube of a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases, and said conduit includes longitudinalreinforcement against longitudinal stretching of said conduit.
 34. Abreathing circuit component as claimed in claim 33 wherein saidlongitudinal reinforcement includes a plurality of longitudinallyextending threads spaced around the perimeter of the conduit wall, eachsaid thread aligned substantially parallel with the overall axis of saidtube.
 35. A breathing circuit component including an inlet, an outletand an enclosing wall defining a gases passageway between said inlet andsaid outlet, at least a region of said wall being of a material thatallows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, and wherein said gases passageway isan expiratory conduit and said region or regions is or are distributedover the length of said conduit, and said conduit includes at least onehelically wound polymer tape or strip, part or all of said strip beingof a material that allows the passage of water vapour without allowingthe passage of liquid water or respiratory gases, respective edges ofadjacent turns of said strip being adjoining or overlapping and bonded,and said conduit includes lateral reinforcement against crushing, andwherein said lateral reinforcement is a helical bead or a series ofannular ring beads or ribs distributed over the length of said conduit,and said conduit includes a further wall of a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases, and said further wall is spaced from said enclosingwall by at least said helical bead.
 36. A breathing circuit componentincluding an inlet, an outlet and an enclosing wall defining a gasespassageway between said inlet and said outlet, at least a region of saidwall being of a material that allows the passage of water vapour withoutallowing the passage of liquid water or respiratory gases, and whereinsaid gases passageway is an expiratory conduit and said region orregions is or are distributed over the length of said conduit, andwherein said conduit includes at least one longitudinal strip, part orall of said strip being of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, said strip or strips extending parallel to the axis of saidconduit, edges of said strip or strips adjoining or overlapping to forman enclosed tube and bonded, and said conduit includes lateralenforcement against crushing, and wherein said lateral reinforcement isa helical bead or a series of annular ring beads or ribs distributedover the length of said conduit, and said conduit includes a furtherwall of a material that allows the passage of water vapour withoutallowing the passage of liquid water or respiratory gases, and saidfurther wall is spaced from said enclosing wall by at least said helicalbead.
 37. A breathing circuit component including an inlet, an outletand an enclosing wall defining a gases passageway between said inlet andsaid outlet, at least a region of said wall being of a material thatallows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, and wherein said gases passageway isan expiratory conduit and said region or regions is or are distributedover the length of said conduit, and wherein said conduit is a blownfilm tube of a material that allows the passage of water vapour withoutallowing the passage of liquid water or respiratory gases, and saidconduit includes lateral reinforcement against crushing, and whereinsaid lateral reinforcement is a helical bead or a series of annular ringbeads or ribs distributed over the length of said conduit, and saidconduit includes a further wall of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, and said further wall is spaced from said enclosing wall by atleast said helical bead.
 38. A breathing circuit limb having bothinspiratory and expiratory gases passageways, each having a respectiveinlet and outlet and a wall defining a gases passageway extending fromsaid inlet to said outlet, at least a region of the wall of theexpiratory conduit being of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, and wherein one said gases passageway is defined by an innerconduit, said inner conduit is disposed substantially coaxially withinan external surrounding conduit, and the other of said gases passagewaysis defined between the inner and outer conduits, and wherein saidconduit includes at least one longitudinal strip, part or all of saidstrip being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases, saidstrip or strips extending parallel to the axis of said conduit, edges ofsaid strip or strips adjoining or overlapping to form an enclosed tubeand bonded, and said conduit includes longitudinal reinforcement againstlongitudinal stretching of said conduit.
 39. A breathing circuit limb asclaimed in claim 38 wherein said longitudinal reinforcement includes aplurality of longitudinally extending threads spaced around theperimeter of the conduit wail, each said thread aligned substantiallyparallel with the overall axis of said tube.
 40. A breathing circuitlimb having both inspiratory and expiratory gases passageways, eachhaving a respective inlet and outlet and a wall defining a gasespassageway extending from said inlet to said outlet, at least a regionof the wall of the expiratory conduit being of a material that allowsthe passage of water vapour without allowing the passage of liquid wateror respiratory gases, and wherein one said gases passageway is definedby an inner conduit, said inner conduit is disposed substantiallycoaxially within an external surrounding conduit, and the other of saidgases passageways is defined between the inner and outer conduits, andwherein said conduit is a brown film tube of a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases, and said conduit includes longitudinal reinforcementagainst longitudinal stretching of said conduit.
 41. A breathing circuitlimb as claimed in claim 40 wherein said longitudinal reinforcementincludes a plurality of longitudinally extending threads spaced aroundthe perimeter of the conduit wail, each said thread alignedsubstantially parallel with the overall axis of said tube.
 42. Abreathing circuit limb having both inspiratory and expiratory gasespassageways, each having a respective inlet and outlet and a first walldefining a gases passageway extending from said inlet to said outlet, atleast a region of the wall of the expiratory conduit being of a materialthat allows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, and wherein one said gases passagewayis defined by an inner conduit, said inner conduit is disposedsubstantially coaxially within an external surrounding conduit, and theother of said gases passageways is defined between the inner and outerconduits, and wherein said conduit includes at least one helically woundpolymer tape or strip, part or all of said strip being of a materialthat allows the passage of water vapour without allowing the passage ofliquid water or respiratory gases, respective edges of adjacent turns ofsaid strip being adjoining or overlapping and bonded, and said conduitincludes lateral reinforcement against crushing, and wherein saidlateral reinforcement is a helical bead or a series of annular ringbeads or ribs distributed over the length of said conduit, and saidconduit includes a further wall of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, and said further wall is spaced from said first wall by at leastsaid helical bead.
 43. A breathing circuit limb having both inspiratoryand expiratory gases passageways, each having a respective inlet andoutlet and a first wall defining gases passageway extending from saidinlet to said outlet, at least a region of the wall of the expiratoryconduit being of a material that allows the passage of water vapourwithout allowing the passage of liquid water or respiratory gases, andwherein one said gases passageway is defined by an inner conduit, saidinner conduit is disposed substantially coaxially within an externalsurrounding conduit, and the other of said gases passageways is definedbetween the inner and outer conduits, and wherein said conduit includesat least one longitudinal strip, part or all of said strip being of amaterial that allows the passage of water vapour without allowing thepassage of liquid water or respiratory gases, said strip or stripsextending parallel to the axis of said conduit, edges of said strip orstrips adjoining or overlapping to form an enclosed tube and bonded andsaid conduit includes lateral reinforcement against crushing, andwherein said lateral reinforcement is a helical bead or a series ofannular ring beads or ribs distributed over the length of said conduit,and said conduit includes a further wall of a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases, and said further wall is spaced from said first wallby at least said helical bead.
 44. A breathing circuit limb having bothinspiratory and expiratory gases passageways, each having a respectiveinlet and outlet and a first wall defining a gases passageway extendingfrom said inlet to said outlet, at least a region of the wall of theexpiratory conduit being of a material that allows the passage of watervapour without allowing the passage of liquid water or respiratorygases, and wherein one said gases passageway is defined by an innerconduit, said inner conduit is disposed substantially coaxially withinan external surrounding conduit, and the other of said gases passagewaysis defined between the inner and outer conduits, and wherein saidconduit is blown film tube of a material that allows the passage ofwater vapour without allowing the passage of liquid water or respiratorygases, and said conduit includes lateral reinforcement against crushing,and wherein said lateral reinforcement is a helical bead or a series ofannular ring beads or ribs distributed over the length of said conduit,and said conduit includes a further wall of a material that allows thepassage of water vapour without allowing the passage of liquid water orrespiratory gases, and said further wall is spaced from said first wallby at least said helical bead.